WASHINGTON — The global shipping industry should consider placing armed guards on its boats to ward off pirates who have become increasingly violent, the U.S. military commander who oversees the African coastline said Friday. Gen. David Petraeus who came to the Capitol to talk about a wide variety of issues told a House committee Friday that just trying to outrun or block pirates from boarding cargo ships isn't enough to deter sea bandits off the Somali coast who are becoming more aggressive.